The present invention relates to a centrifugal air compressor, which is provided with a rotary shaft supported by a magnetic bearing and a rotary vane that is encompassed by a pressure volute while being connected to the rotary shaft.
As is well known, centrifugal air compressors are structured so as to compress intake air by rotating rotary vanes. Therefore, a rotary shaft for rotating the rotary vanes must be supported by a structure capable of withstanding high-speed rotation. Many of the thus structured centrifugal air compressors adopt a magnetic bearing capable of supporting the rotary shaft in a non-contact manner as a bearing system for supporting the rotary shaft.
Some of these compressors are used outdoors, for example, as on-vehicle compressors. In this instance, ambient temperatures are in a very wide range from −40° C. to 80° C. In an environment where temperatures are 0° C. or lower, moisture contained in outside air freezes up in a narrow clearance between a rotary vane and the inner wall of a pressure volute, and the rotary vane can be adhered to the pressure volute due to the congelation. The above situation is also found in a case where compressors are used in those of radiators and refrigerators/freezers.
For example, Japanese Laid-Open Patent Publication No. 4-287896 discloses a pump in which, if a rotor is adhered to other members by deposits, a magnetic bearing is used to vibrate the rotor forcibly, thereby releasing the rotor from the adhesion.
In the pump described in Japanese Published Laid-Open Patent Publication No. 4-287896, even with a gas high in reactivity, if there is a deposit substance contained in the gas exhausted from a discharge system for etching apparatus used in semiconductor manufacturing, adhesion of a rotor is highly likely to be eliminated by forcibly vibrating the rotor by use of a magnetic bearing. However, in the case where a rotary vane is adhered to a pressure volute due to a congelation, the state of which is closer to coagulation than deposition, it is less likely that adhesion of a rotary vane is eliminated through vibration by a magnetic bearing. In the case where adhesion of a rotary vane cannot be reliably eliminated, the starting performance of the centrifugal air compressors is significantly degraded.